Metal extrusion presses are well known in the art, and are used for forming extruded metal products having cross-sectional shapes that generally conform to the shape of the extrusion dies used. A typical metal extrusion press comprises a generally cylindrical container having an outer mantle and an inner tubular liner. The container serves as a temperature controlled enclosure for a billet during extrusion. An extrusion ram is positioned adjacent one end of the container. The end of the extrusion ram abuts a dummy block, which in turn abuts the billet allowing the billet to be advanced through the container. An extrusion die is positioned adjacent the opposite end of the container.
During operation, once the billet is heated to a desired extrusion temperature (typically 800-900° F. for aluminum), it is delivered to the extrusion press. The extrusion ram is then activated to abut the dummy block thereby advancing the billet into the container and towards the extrusion die. Under the pressure exerted by the advancing extrusion ram and dummy block, the billet is extruded through the profile provided in the extrusion die until all or most of the billet material is pushed out of the container, resulting in the extruded product.
In order to attain cost-saving efficiency and productivity in metal extrusion technologies, it is important to achieve thermal alignment of the extrusion press. Thermal alignment is generally defined as the control and maintenance of optimal running temperature of the various extrusion press components. Achieving thermal alignment during production of extruded product ensures that the flow of the extrudable material is uniform, and enables the extrusion press operator to press at a higher speed with less waste.
As will be appreciated, optimal billet temperature can only be maintained if the container can immediately correct any change in the liner temperature during the extrusion process, when and where it occurs. Often all that is required is the addition of relatively small amounts of heat to areas that are deficient.
A number of factors must be considered when assessing the thermal alignment of an extrusion press. For example, the whole of the billet of extrudable material must be at the optimum operating temperature in order to assure uniform flow rates over the cross-sectional area of the billet. The temperature of the liner in the container must also serve to maintain, and not interfere with, the temperature profile of the billet passing therethrough.
Achieving thermal alignment is generally a challenge to an extrusion press operator. During extrusion, the top of the container usually becomes hotter than the bottom. Although conduction is the principal method of heat transfer within the container, radiant heat lost from the bottom surface of the container rises inside the container housing, leading to an increase in temperature at the top. As the front and rear ends of the container are generally exposed, they will lose more heat than the center section of the container. This may result in the center section of the container being hotter than the ends. As well, the temperature at the extrusion die end of the container tends to be slightly higher compared to the ram end, as the billet heats it for a longer period of time. These temperature variations in the container affect the temperature profile of the liner contained therein, which in turn affects the temperature of the billet of extrudable material. The temperature profile of the extrusion die generally conforms to the temperature profile of the liner, and the temperature of the extrusion die affects the flow rate of extrudable material therethrough. Although the average flow rate of extrudable material through the extrusion die is governed by the speed of the ram, flow rates from hotter sections of the billet will be faster compared to cooler sections of the billet. The run-out variance across the cross-sectional profile of a billet can be as great as 1% for every 5° C. difference in temperature. This can adversely affect the shape of the profile of the extruded product. Control of the temperature profiles of the liner and of the container is therefore of great importance to the efficient operation of the extrusion process.
One approach to achieving such temperature profile control of the liner and the container involves introducing cooling to the container. Cooling in extrusion press containers has been previously described. For example, U.S. Pat. No. 5,678,442 to Ohba et al. discloses an extruder having a cylindrical container into which a billet is loaded; a two-piece seal block disposed on an end surface of the container at an extruding stem side; a vacuum deaerating hole formed in the seal block; and a fixed dummy block, having an internal cooling function, fixed to an end of the extruding stem, wherein the seal block is allowed to be opened and closed in a direction perpendicular to the axial direction of the container and the seal block comes in close contact with an outer surface of the extruding stem and the end surface of the container when the seal block is closed.
U.S. Pat. No. 4,829,802 to Baumann discloses an apparatus comprising a region of an extrusion chamber immediately ahead of an extrusion die that is cooled by placing a cooling ring between the bore of an extrusion cylinder in which a ram piston operates. The cooling ring may be a unitary structure, or a multi-part structure, in which an independent inner ring is located within the cooling ring. For mechanical strength, a prestressing outer ring is shrink-fitted around the cooling ring. The outer ring is retained, for example by screws, on a cylinder within which the extrusion chamber is located. The cooling fluid may be water, a vaporizable liquid, or a gas, and is separated from the billet within the extrusion chamber.
Improvements are generally desired. It is therefore an object at least to provide a novel extrusion press container and a mantle for same.